The present invention relates to a forming machine with a shearing device.
In forming machines with one or more forming stations, a portion sheared off from a bar is often fed to the first forming station for forming. The shearing of the bar normally takes place in a separate shearing station by means of a fixed bar cutter and a cropping cutter which is displaceable with respect to said bar cutter and is moved back and forth by a shearing carriage. Various possibilities are known for the design of the bar cutter and the cropping cutter.
In cold forming machines, for example, closed round cutters are used as the bar cutter and cropping cutter. The bar to be sheared is pushed into the opening of the bar cutter and cropping cutter and the cropping cutter is subsequently rapidly displaced transversely with respect to the bar, whereby a portion is sheared off from the bar. One disadvantage of the two closed round cutters is that the pushing in of the bar to be sheared involves friction. Furthermore, they cannot be readily used in hot forming machines, since in these machines an unnecessary heat dissipation from the bar should be prevented and the falling out of the scale present should not be hindered.
In hot forming machines, the bar cutter and the cropping cutter are normally designed as half-cutters, i.e. as cutters which bear against the bar only over part of its circumference, the bar to be sheared being held during shearing between the half-cutters and clamping jaws. After shearing, the clamping jaws are moved away for advancing and releasing the bar. For centering the bar, a separate, relatively inflexible centering device is provided. It is disadvantageous that if the position of the portion fed in has to be corrected with respect to the center of the first forming station to optimize the first forming step, many individual parts, namely the cropping cutter, the bar cutter, the clamping jaws and the centering device, have to be reset for the consequently necessary realignment of the center of the cropping cutter and of the bar cutter.
Independently of a forming machine, U.S. Pat. No 5,062,336 discloses a shearing device for shearing bars in which the fixed cutter and the cutter which is displaceable with respect to it respectively comprise two half-cutters.
Likewise independently of a forming machine, U.S. Pat. No. 4,152,959 discloses a shearing device for shearing bars in which the fixed cutter comprises two half-cutters which can be spread apart, while the cutter which is displaceable with respect to said fixed cutter is designed as a closed round cutter. The spreading apart of the half-cutters is very restricted, however, so that the falling out of any scale present is hindered.
U.S. Pat. No. 5,690,010 discloses a shearing device of a forming machine which has a slit round cutter, comprising a fixed bar cutter which is designed as a half-cutter and a clamping piece which is movable with respect to said bar cutter, and also a cropping cutter which interacts with the slit round cutter, is displaceable with respect to it and is designed as a closed round cutter. The clamping piece is adjustable between a position clamping the bar to be sheared and a position not clamping the bar to be sheared, but it is not envisaged for said clamping piece to be moved completely away from the bar, so that the falling out of any scale present is hindered.
In view of the disadvantages of the previously known shearing devices described above, the invention is based on the following object. It is intended to provide a forming machine with a shearing device of the type mentioned at the beginning in which the shearing device makes it possible for the bar which is to be sheared to be pushed in without unnecessary friction and for any scale present to fall out, and also for the setting of the center of the cropping cutter and of the bar cutter to be possible in a simple way.
The essence of the invention is the following: A forming machine comprises a shearing device which has a slit round cutter, comprising a fixed bar cutter which is designed as a half-cutter and a centering and clamping piece which is movable with respect to said bar cutter, and also a cropping cutter which interacts with the slit round cutter, is displaceable with respect to it and is designed as a closed round cutter. The forming machine further comprises control means with which the centering and clamping piece is movable in a controlled manner between a centering position, in which, during operation, it centers a bar to be sheared without clamping it, a release position, in which it is moved completely away from the bar to be sheared, and a clamping position, in which it clamps the bar to be sheared.
The centering of a bar to be sheared takes place according to the invention by the centering and clamping piece in the centering position together with the bar cutter. During shearing, the bar to be sheared is held between the bar cutter and the centering and clamping piece in the clamping position and in the cropping cutter. After shearing, the centering and clamping piece is moved away from the bar cutter into the release position, so that the bar can be advanced again without unnecessary friction. Furthermore, the removal of the centering and clamping piece from the bar in hot forming machines makes it possible for scale to fall out and prevents avoidable heat dissipation from the bar. Both the centering and the clamping of the bar take place by means of the centering and clamping piece, so that it is possible to dispense with an additional centering device. For setting the center of the cropping cutter and of the bar cutter, only the cropping cutter in the form of a closed round cutter and the slit round cutter formed by the bar cutter and the centering and clamping piece have to be accurately positioned.